In a large mixing bowl, combine rolled oats, chia seeds, brown sugar, mashed bananas, vanilla extract, cinnamon, salt, and milk. Stir well until everything is fully incorporated.
Cover the bowl or divide the mixture into individual jars or containers. Seal and refrigerate for at least 4 hours, preferably overnight, allowing the oats to absorb the liquid.
In the morning, stir the oats and add extra milk if needed to adjust consistency.
Top with sliced bananas, chopped nuts, or a drizzle of honey for added flavor and texture. Enjoy cold or warm!